Field of the Invention
The present invention relates to a solid-state imaging apparatus having a focus detecting device mounted thereon, and an imaging system using the same.
Description of the Related Art
In Japanese Patent Application Laid-Open No. 2011-60815, there is disclosed a focus detecting device of a phase difference detection system in which focus detection pixels (pixels for autofocus (AF)) are disposed on an imaging surface. The phase difference detection system is a focus detection system in which a focus adjusting state of an optical system is detected by detecting an image interval (phase difference) between focus detection pixels. The focus detection pixels of the focus detecting device each include a light shielding layer for shielding a part of an opening in a photoelectric conversion unit for the purpose of selectively introducing a light flux that passes through the optical system into photoelectric conversion units of the focus detection pixels.
In Japanese Patent Application Laid-Open No. 2013-102383, there is disclosed a solid-state imaging apparatus that improves a signal-to-noise (S/N) ratio of signals of AF pixels by setting an amplification factor of a signal from an imaging pixel and an amplification factor of a signal from an AF pixel of a phase difference detection system to be different from each other.
The focus detection pixels of a solid-state imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2011-60815 each include the light shielding layer for shielding a part of the opening. This narrows an opening in the focus detection pixel compared with an opening in the imaging pixel, and thus, an output signal of the focus detection pixel tends to be smaller than that of the imaging pixel. Therefore, there are cases in which adequate sensitivity for detecting a focus cannot be obtained.
One way to improve sensitivity of detecting a focus in such a structure is, as disclosed in Japanese Patent Application Laid-Open No. 2013-102383, to increase the amplification factor of the AF pixel. However, when the amplification factor is increased, noise that is output together with a signal from the pixel may also be amplified, and thus, depending on the source of the noise, the S/N ratio may not be improved. In particular, when the brightness is low, the S/N ratio of a signal that is output from the pixel is low, and thus, a problem in that the focus detection performance is lowered may arise. On the other hand, with regard to the imaging pixel, not only higher sensitivity but also higher resolution imaging is required.